A regenerative heating plant for a blast furnace has several, normally three, cowper-type regenerative-heating stoves connected via respective hot-blast valves to a common hot-blast main itself connected to the tuyeres of the furnace. The stoves each have a small-section combustion chamber that is mainly empty and a larger heating chamber that is filled with checker brick. The two chambers are vertically elongated and communicate at their upper ends at the stove dome. The lower end of the heating chamber can be connected via a respective stack valve to an exhaust line leading via treatment scrubbers to the smokestack, or via cold-blast valve to a cold-blast line pressurized with ambient air. The lower region of the combustion chamber has a port connected to the respective hot-blast valve and the bottom of this combustion chamber is connected to or has a burner.
During firing of the stove the heating chamber is isolated by the respective cold-blast valve from the cold-blast main and the respective stack valve is open so the heating chamber is connected to the stack, the hot-blast valve is closed, and the burner is fired so that combustion takes place in the combustion chamber and the hot combustion gases pass through the checker brick in the heating chamber and heat same to 900.degree. C. to 1300.degree. C., these gases then exiting to the stack. For regenerative heating the burner is isolated by its valve, the stack valve is closed, the cold-blast is open, and the hot-blast valve is open. Ambient air is thereby forced up through the hot brick and down through the hot combustion chamber, whence it passes out through the hot-blast valve and through the hot-blast main to the tuyeres of the furnace. Several such stoves are provided so that two can be firing while one is used. Thus the furnace can operate continuously with regeneratively heated air.
The hot-blast valves are therefore subjected to considerable stress, being heated often as high as 1400.degree. C. As a result massive gate valves are employed often with flow cross sections of 1 m.sup.2. Cast iron for the valves was superseded by cast steel valve housings with copper seats constructed with passages through which a coolant can circulate. Even such valves normally only had a service life of a few weeks.
The present-day capacity of welding steel has made it possible for weld steel to be used in such valves, giving substantially longer service lives. Normally the valve housing is covered with a refractory material to shield it from the high heat it is exposed during firing of the respective stove.
This welded construction is under considerable stress which can lead to cracking and leakage where the valve body joins the pocket that the gate is retracted into when the hot-blast valve is open. These stresses are caused by temperature gradients induced in the metal of the valve housing when the system is working.
Furthermore, a substantial amount of heat is lost from the hot blast because of the large cooling surface. In addition the energy consumption to cool the seat is considerable and objectionable because no useful work is done.